diff --git a/strings/birthday.go b/strings/birthday.go
new file mode 100644
index 0000000..18e8b67
--- /dev/null
+++ b/strings/birthday.go
@@ -0,0 +1,49 @@
+package strings
+
+import (
+	"time"
+)
+
+type Birthday string
+
+// ToAge returns the age of the birthday
+// Example:
+//
+//	input: "2020-01-01", today: 2023-10-01 result: [3, 9]
+func (b Birthday) ToAge(todayTime time.Time) ([2]int, error) {
+	var (
+		layout       = "2006-01-02"
+		birthdayTime time.Time
+		years        int
+		months       int
+		err          error
+	)
+
+	if birthdayTime, err = time.Parse(layout, string(b)); err != nil {
+		return [2]int{}, err
+	}
+
+	// Calculate the difference in years
+	years = todayTime.Year() - birthdayTime.Year()
+
+	// If today's month is less than birthday's month, subtract a year
+	// Or if they are on the same month, but today's day is less than birthday's day, also subtract a year
+	if todayTime.Month() < birthdayTime.Month() ||
+		(todayTime.Month() == birthdayTime.Month() && todayTime.Day() < birthdayTime.Day()) {
+		years--
+	}
+
+	// Calculate the difference in months
+	if todayTime.Month() >= birthdayTime.Month() {
+		months = int(todayTime.Month() - birthdayTime.Month())
+	} else {
+		months = int(todayTime.Month() + 12 - birthdayTime.Month())
+	}
+
+	// If today's day is less than birthday's day, subtract a month
+	if todayTime.Day() < birthdayTime.Day() {
+		months--
+	}
+
+	return [2]int{years, months}, nil
+}
diff --git a/strings/birthday_test.go b/strings/birthday_test.go
new file mode 100644
index 0000000..094087e
--- /dev/null
+++ b/strings/birthday_test.go
@@ -0,0 +1,17 @@
+package strings
+
+import (
+	"testing"
+	"time"
+)
+
+func TestBirthday_ToAge(t *testing.T) {
+	b := Birthday("1990-01-01")
+	today := time.Date(2023, 10, 1, 0, 0, 0, 0, time.UTC)
+	expected := [2]int{33, 9}
+	if result, err := b.ToAge(today); err != nil {
+		t.Errorf("ToAge(%v) returned an error: %v", b, err)
+	} else if result != expected {
+		t.Errorf("ToAge(%v) = %v, expected %v", b, result, expected)
+	}
+}